The present invention is directed to a compressor unit, and more particularly, to a rotary compressor system having a housing with a motor and a fluid accumulator located on the low pressure side and an oil sump located on the high pressure side.
In general, a closed rotary compressor forms a part of a heating and air conditioning system (HVAC) refrigerant cycle. A compressor or compressor unit, as used herein, commonly includes a number of components such as a housing, a compressor portion, a motor having a stator and a rotor, bearings, a suction port, a discharge port, an oil sump and an accumulator. Other components may be included depending upon the design of the compressor. Various types of compressors can be used in such applications including reciprocating piston compressors, scroll compressors, rotary compressors and screw compressors. The conventional rotary compressor is a sliding vane compressor having an electric motor arranged in an upper portion of a shell or casing. Compression is accomplished by an impeller or roller which is located on and is rotated by a shaft, at least a portion of which includes an eccentric arrangement and which shaft is coupled to the motor 20. An accumulator is arranged on a side portion of the rotary compressor. As the roller rotates within a cylindrical chamber formed within housing, the impeller or roller contacts the walls of housing. The eccentric rotation of the roller causes refrigerant gas entering into the chamber through suction port to be compressed before it exits an exhaust port (not shown).
Another example of a rotary compressor uses a plurality of blades that rotate on a shaft, thereby providing compression of gas. And the invention is not restricted to rotary compressors. For example, a scroll compressor that utilizes an orbiting scroll rotating in an eccentric manner in a spatial relationship to a fixed scroll may also be used.
These compressors may be high pressure systems or low pressure systems in which the motor and compressor portion of the compressor are contained in a single chamber within a housing.
A high pressure system employs a housing that includes a compressor portion and a motor, and typically an accumulator external to the housing. The motor is contained in a chamber in the housing that is maintained at a high pressure. The housing is provided with a suction tube that draws refrigerant into the compression volume of the compressor portion. The compressed fluid is then discharged into the chamber containing the motor, where the high pressure fluid cools the motor before leaving the housing through a discharge tube. The chamber containing the motor is thus maintained at the compressor discharge pressure.
A low pressure system also employs a housing that includes a compressor portion and a motor. The motor is contained in chamber in the housing that is maintained at low pressure, that is, at compressor suction pressure. In this arrangement, the suction tube draws refrigerant into the chamber where the refrigerant cools the motor before the refrigerant is drawn into the compressor suction port, and thence into the compression volume of the compressor portion where it is compressed. The compressed fluid then is expelled from the compression through the discharge port.
These compressors typically employ an accumulator, such as is shown in FIG. 2, which typically are external to the compressor. The accumulator accumulates lubricant and refrigerant, which may be in the form of liquid, gas or both phases. Ideally, the liquid phase includes solely lubricant and the gaseous phase includes solely refrigerant. However, more typically, the liquid phase also includes refrigerant and the gaseous phase frequently includes lubricant.
There are a number of problems associated with these compressor systems. In high pressure systems, the compressed gas from the discharge port of the compressor is at an elevated temperature, and may provide inadequate cooling of the motor in certain situations, such as during long duty cycles in operating environments with high ambient temperatures. This can cause motor overheating which can lead to premature motor failures and shortened operational life of the compressor. In low pressure systems, difficulties arise because lubrication must be provided to the compressor portion operating at high pressure while preventing the compressed fluid from leaking across the compressor""s sealing surfaces. Difficulties can also arise when trying to separate the lubricating oil from the compressed fluid. The lubricant mixed with liquid refrigerant can lower the efficiency of the unit and in extreme cases can result in slugging, discussed below. The liquid refrigerant mixed with lubricant can adversely affect the lubrication of the system as the refrigerant tends to wash the lubricant from the surfaces requiring lubrication, resulting in increased wear and in extreme cases, failure as parts seize. An external accumulator is frequently employed to assist in collecting excess fluid and in separating the lubricant from the refrigerant. The external accumulator is required because the suction tube enters the compressor directly at the inlet port. However, with the suction in this position, there can be a problem with slugging. Slugging is a condition that occurs when a mass of liquid, here from the accumulator, enters the compressor portion. This liquid, when in sufficient volume and being incompressible, adversely affects the operation of the compressor and can cause severe damage.
What is desired is a system that can separate the lubricant from the refrigerant while preventing slugging. Such a system provides substantially only gas to the suction port of the compressor portion, while also desirably cooling the motor, thereby preventing overheating, yet still allowing the lubricant to be circulated into the compressor portion to provide effective lubrication of moving and wear parts.
The present invention is a compressor comprising a housing and a sealing means positioned within the housing, defining a first chamber and a second chamber. The first chamber is maintained at a first low pressure, or suction pressure, while the second chamber is maintained at a high pressure. The sealing means is positioned within the housing to define and partition the first chamber and the second chamber and to substantially maintain the pressure differential between the chambers by segregating high pressure fluid in the second chamber from low pressure fluid in the first chamber. The sealing means is designed to prevent leakage of fluid from the second or high pressure chamber to the first or low pressure chamber. The sealing means can seal any leak paths that may exist between the chambers. The first chamber is physically located above the second chamber, and the motor is disposed within the first chamber. A compressor portion, which physically compresses fluids, is located within the second chamber.
Fluid, which may be gas or liquid entrained in the gas, is drawn into the first chamber from the HVAC system through a suction tube inlet physically located at the top of the housing. The fluid entering the housing may contact a deflecting means, which assists in separating it into a gas portion and a liquid portion. The liquid portion is directed downward toward a motor. A first quantity of the gas portion is also directed downward while a second quantity of the gas portion is drawn toward a compressor suction inlet. The liquid portion and the gas portion directed downward toward the motor are circulated through passageways around the motor and adjacent the motor stator to provide cooling for the motor. The liquid portion will collect about the motor components above the sealing means. A space or region is provided in the first chamber to permit the accumulation of a substantial amount of fluid. This space or region forms an internal accumulator for the fluid. Heat generated by the motor windings and transferred to the fluid serves to separate the higher boiling point lubricant from the low boiling point refrigerant, as the refrigerant undergoes a phase transformation into a gas and is drawn through a channeling means to the compressor suction inlet during compressor operation. A fluid connection, such as a bleed hole or tube, through the sealing means allows liquid collected above the sealing means in the internal accumulator to move across this boundary in a controlled manner and flow downward to the compressor suction inlet in the second chamber where it can resupply the sump. The bleed connection can be activated by any one of a number of activating means such as control valves, gravity or hydrostatic pressure of the fluid in the internal accumulator. Most simply, however, the operation of the compressor draws the liquid through the bleed connection to the compressor suction inlet.
Gas channeled toward the compressor suction inlet is generally of high quality, that is to say, it contains little or no lubricant. This refrigerant gas enters the compressor portion through the compressor suction inlet, where it is compressed in the compressor volume. The compressor portion is operably connected to the motor by a motor shaft that passes across the sealing means. Activation of the motor in the typical fashion by starting the motor activates the compressor. During operation of the compressor, lubricant is metered through the bleed hole and is compressed with the refrigerant gas as a compressed fluid. As the compressed fluid exits the compressor before it is discharged, the compressed refrigerant gas and entrained lubricant strikes components such as bearings, sidewalls of the housing in the high pressure region of the compressor or other structures in the second chamber that can separate entrained lubricant from the refrigerant gas. The lubricant, present as droplets or as a mist gathers on these surfaces and flows downward to further resupply the sump. The compressed fluid, from which a substantial amount of lubricant has been removed, then moves upward and is discharged at high pressure through a compressor discharge port. Activation of the motor also causes any lubricant residing in the sump to be drawn upward and delivered to the surfaces of the compressor requiring lubrication.
An advantage of the present invention is that it allows for the elimination of an external accumulator, which results in a savings of space in the restricted area where a compressor is located. The simpler design also eliminates the additional cost associated with the manufacture of the external accumulator and the additional time required to assemble and test the external accumulator to the compressor.
Another advantage of the compressor of the present invention is that it can use the motor of the compressor to substantially eliminate liquid refrigerant when the compressor is not operating. By energizing a winding in the motor after shut down, the winding can be used to heat liquid refrigerant to a temperature sufficient to allow it to transform to a gaseous state, thereby allowing the refrigerant to be moved as a gas from the low pressure region around the motor, returning to circulation within the refrigeration loop.
Yet another advantage of the present invention is that the liquid refrigerant and the lubricant are used to cool the motor during and after its duty cycle. At least some of the heat generated by the motor is utilized to convert the refrigerant from a liquid state back into a gaseous state so that it can be returned to circulation within the system, thereby improving the efficiency of the system and reducing the amount of liquid refrigerant that would otherwise be moved into the system. This also reduces the likelihood of slugging.
Another advantage of the present invention is that the lubricant and the refrigerant can be readily separated in the low pressure side. A portion of the lubricant, substantially free of refrigerant, can then be metered back into the gas flow in a controlled manner through the bleed connection. The lubricant, added to refrigerant during the compression cycle, is substantially separated from the compressed refrigerant by interaction with the physical boundaries in the high pressure chamber before being discharged from the compressor.